1. Field of the Invention
The present invention relates to a torch for thermal spraying of surface coatings and to the coatings obtained by such torch.
2. Description of the Related Art
In recent times, the practice of applying coatings or surface treatments to mechanical parts has increasingly found application in the industry, in view of achieving functional properties that could not be obtained with the substrate and coating materials alone. A typical case relates to materials that have a high mechanical strength and exhibit a non-optimal behavior in wear or corrosion conditions. In this case, a surface treatment or a coating is applied to the surface of the part, to improve its wear or corrosion resistance.
Many deposition technologies are currently available, whose selection depends on the desired coating characteristics, and whose classification is based on a number of criteria, such as the thickness of the coatings to be obtained and the starting physical conditions of the materials used for the coating.
Among these technologies, thermal spraying has become increasingly appreciated due to the considerable variety of materials that can be used for coating and to the characteristics of the obtainable coatings.
The principle of thermal spray technologies consists in supplying energy to the material to be deposited until it melts, and transfer it to the substrate to be coated. Energy may be supplied to the material to be deposited from various sources: energy deriving from combustion between oxygen and a fuel, either in gas form (propane, acetylene, hydrogen) or in liquid form (kerosene) or deriving from recombination of ions in a plasma.
Thermal spray technologies include:                Combustion Flame Spray,        Arc Flame Spray,        Plasma Spray,        HVOF (High Velocity Oxygen Fuel).        
The limitations of thermal spray processes are essentially due to their being line-of-sight processes.
This problem is solved by having the torch handled by a robot or a CNC, so that it can follow even complex outlines.
The coatable pieces may have any size, and the only limitation is the minimum size of cavities and holes: the torch must fit into the holes.
The main drawback of prior art is that it is not adequately applicable to coating of tubes having inner protrusions to be coated: in these instances, the torch has to be small enough to fit into the hole and as a rule, in modern practice, it is connected to a bracket which is in turn connected to the robot that allows it to be introduced in the cylinder to be coated.
The inner protrusions need to be coated all over their surfaces, and this cannot be fully achieved by the prior art torch connected to the bracket and the robot, which can only handle it along its motion axis, the torch being fixed with respect to the axis integral with the robot wrist.